JP4326179B2 - Polymer electrolyte fuel cell - Google Patents

Description

【００７３】
で示されるパーフルオロカーボンスルホン酸の粉末をエチルアルコールに分散した分散液を混合し、触媒ペーストを調製した。
【００７４】
一方、電極のガス拡散層を構成する導電性多孔質基材であるカーボンペーパーを撥水処理した。厚み３６０μｍのカーボン不織布１１（東レ（株）製のＴＧＰ−Ｈ−１２０）を、テトラフルオロエチレンとヘキサフルオロプロピレンの共重合体（ＦＥＰ）の水性分散液（ダイキン工業（株）製のネオフロンＮＤ−１）に含浸し、乾燥した後、３８０℃で３０分間加熱することによって、撥水性を付与した。
【００７５】
次に、炭素粉末（電気化学工業（株）製のアセチレンブラックＨＳ−１００、一次粒径：５３ｎｍ、比表面積：３７ｍ²／ｇ、ＤＢＰ吸油量：２００ｃｃ／１００ｇ）を、上記ネオフロンＮＤ−１に分散し、炭素粉末とＦＥＰの混合重量比が８７：１３であるペーストを得た。このペーストを前述の撥水処理を施したカーボン不織布１１の表面に塗布し、乾燥した後、３８０℃で３０分間加熱することによって、炭素粉末層１２を形成した。このとき、炭素粉末層１２の一部は、カーボン不織布１１の中に埋まって入り込んでいた。このようにして、カーボン不織布１１と炭素粉末層１２からなるガス拡散層１３を作製した。
【００７６】
この炭素粉末層１２の上に、前述の触媒ペーストをスクリーン印刷法を用いて塗布し、触媒層１４を形成した。このようにして、触媒層１４、炭素粉末層１２およびカーボン不織布１１からなる電極１６を作製した。
電極中に含まれる白金量は０．５ｍｇ／ｃｍ²、パーフルオロカーボンスルホン酸の量は１．２ｍｇ／ｃｍ²とした。この電極１６をアノードおよびカソードの両方に使用する。
【００７７】
ここで、ガス拡散層に用いた炭素粉末（電気化学工業（株）製のアセチレンブラックＨＳ−１００）の撥水性は、触媒層に用いた炭素粉末（ＶｕｌｃａｎＸＣ７２）の撥水性よりも高いものであった。なお、撥水性の評価は、以下の方法で行った。
【００７８】
まず、ドクターブレードを用いて被検物である炭素粉末の粒子をガラス表面に平らに塗りつけ、そこに表面張力（ｍＮ／ｍ）の異なる溶液を滴下した。滴下した溶液が炭素粒子の塗布面から内部方向に染み込むか、または塗布面で弾かれるかを観察する。表面張力の小さい溶液を弾く炭素粒子の方が、撥水性が強い。例えば、水およびエタノールの表面張力は、それぞれ７２および２２（ｍＮ／ｍ）であり、水は弾くがエタノールは染み込む炭素粒子の撥水性より、水もエタノールも共に弾く炭素粒子の撥水性の方が高いといえる。以上の評価結果を表１に示す。表１には、各種の炭素粒子の物性と、上記撥水性評価の結果を示した。撥水性の欄に記載の値は、炭素粒子が弾く溶液の最も小さい表面張力（ｍＮ／ｍ）である。
【００７９】
次に、前述の電極１６より５ｍｍ大きい外寸を有する水素イオン伝導性高分子電解質膜（米国Ｄｕ Ｐｏｎｔ社製Ｎａｆｉｏｎ１１２）１５の両面に、一対の電極１６を、触媒層１４が電解質膜１５の側に接するようにホットプレスで接合し、ＭＥＡ１７を得た。
このＭＥＡ１７を導電性セパレータ板で挟み込んで単電池を得た。導電性セパレータ板は、カーボン粉末材料を冷間プレス成形して得られるカーボン板に、フェノール樹脂を含浸させて硬化することによって得た。このように樹脂を含浸させることにより、ガスシール性が改善された。さらに、前記カーボン板に切削加工を施すことにより、ガス流路を形成した。
【００８０】
図６および７は、表面にガス流路（溝）を形成した導電性セパレータ板の概略平面図である。図６は、導電性セパレータの表面に形成した燃料ガス用ガス流路の形状を示しており、裏面には同一形状の酸化剤ガス用ガス流路を形成した。図７は、燃料ガス用ガス流路を形成した導電性セパレータ板の裏面に形成された冷却水用流路の形状を示したものである。セパレータは１０ｃｍ×２０ｃｍ×４ｍｍの寸法を有しており、ガス流路を構成する溝部２１は幅２ｍｍで深さ１．５ｍｍの凹部であり、この部分をガスが流通する。また、ガス流路間のリブ部２２は幅１ｍｍの凸部である。また、酸化剤ガスのマニホルド孔（注入口２３ａ、出口２３ｂ）と、燃料ガスのマニホルド孔（注入口２４ａ、出口２４ｂ）と、冷却水のマニホルド孔（注入口２５ａ、出口２５ｂ）を形成した。また、ポリイソブチレンに導電性カーボンを分散させた導電性のガスシール部２６を形成した。
【００８１】
以上のように作製した図５に示すＭＥＡ１７を、図６に示す２枚の導電性セパレータ板で、一方の燃料ガス用ガス流路がＭＥＡ１７に面し、他方の酸化剤ガス用ガス流路がＭＥＡ１７に面するように挟んで接合し、単電池Ａを得た。また、図５に示すＭＥＡ１７を、図７に示す２枚の導電性セパレータ板で、一方の燃料ガス用ガス流路がＭＥＡ１７に面し、他方の冷却水用流路がＭＥＡ１７に面するように挟んで接合し、単電池Ｂを得た。
【００８２】
次に、単電池Ａと単電池Ｂを１個ずつ交互に積層し、合計で５０個の単電池を積層して積層体を得た。この積層体の両端に金属製の集電板、電気絶縁材料からなる絶縁板、および端板を順に重ね合わせてスタックを得た。そして、スタックを貫通させたボルトとナットにより、両端板を締結して電池モジュールを得た。このときの締結圧はセパレータ板に対して１０ｋｇｆ／ｃｍ²とした。スタックを締結するための締結ロッド部は、ガスの給排出口が開いている側面とは異なる側面に設けた。このようにして作製した電池モジュールを燃料電池１（比較例７）とした。
【００８３】
次に、異なる構成のＭＥＡを有する燃料電池を作製した。比較例７と異なる炭素粉末を、触媒層とガス拡散層に配置して燃料電池２〜８（実施例１および比較例７〜１３）を作製した。炭素粉末以外の構成要素は、比較例７と同一とした。用いた炭素粉末の種類と物性を表１に示す。また、燃料電池のカソードおよびアノードに用いた炭素材料番号、電池構成および電池番号を表２に示す。なお、表１の粒径は一次粒子の粒径である。
【００８４】
【表１】

【００８５】
【表２】

【００８６】
[評価]
以上の実施例１および比較例７〜１３で得られた燃料電池１〜８について、放電特性試験を行った。
燃料電池のアノードに純水素ガスを供給し、カソードに空気を供給し、電池温度を７５℃に維持した。そして、燃料ガス利用率（Ｕｆ）を７０％、空気利用率（Ｕｏ）を２０％とした。ガスの加湿は、燃料ガスを８５℃、空気を６５〜７０℃の加湿バブラーに通して行った。
【００８７】
図８に、本発明の実施例に係る燃料電池２と、比較例に係る燃料電池１、３および６の放電特性を示した。また、図９に、本発明の比較例に係る燃料電池４および５と、７〜８の放電特性を示した。図８および図９から、本発明の燃料電池は比較例の燃料電池と較べて、優れた特性を有することがわかる。
【００８８】
参考例３〜５
触媒層およびガス拡散層からなる電極を作製した。アセチレンブラック粉末に、平均粒径約３０Åの白金粒子を２５重量％担持したものを電極用の触媒として用いた。この触媒粉末をイソプロパノールに分散させた分散液に、上記化学式（１）で示したパーフルオロカーボンスルホン酸の粉末をエチルアルコールに分散した分散液を混合し、触媒ペーストを得た。
【００８９】
一方、電極のガス拡散層を構成する導電性多孔質基材であるカーボンペーパーを撥水処理した。フッ素樹脂の水性分散液（ダイキン工業（株）製のネオフロンＮＤ−１）にアセチレンブラックを分散してスラリー（フッ素樹脂固形分：アセチレンブラック＝１：１（重量比））を得た。このスラリーを、厚み３６０μｍのカーボン不織布（東レ（株）製のＴＧＰ−Ｈ−１２０）１１に塗布し、乾燥した後、３８０℃で３０分間加熱することで、撥水性を有するガス拡散層を得た。このとき、ガス拡散層のガス拡散性と導電性を維持するために、乾燥後のガーレー定数が１〜６０（秒/１００ｍＬ）となるように、スラリーの塗布量を調整した。なお、ガーレー定数の評価は、ＪＩＳ−Ｐ８１１７に準拠した。このガーレー定数が小さいとガス拡散層が粗となり、導電性が悪化する。逆に、ガーレー定数が大きいとガス拡散層が密となり、ガス透過性が悪化する。
【００９０】
上述のように撥水性を有するガス拡散層であるカーボン不織布の一方の面に、上記触媒ペーストをスクリーン印刷法を用いて塗布することで触媒層を形成した。このとき、触媒層の一部は、カーボン不織布の中に埋まって入り込んでいた。このようにして、触媒層３２とガス拡散層３１を有する電極３３を得た（図１０参照）。電極中に含まれる白金量は０．５ｍｇ／ｃｍ²、パーフルオロカーボンカーボンスルホン酸の量は１．２ｍｇ／ｃｍ²となるよう調整した。
【００９１】
次に、電極３３より２ｍｍ大きい外寸を有する水素イオン伝導性高分子電解質膜３４の裏表両面に、触媒層３２が電解質膜３４の側に接するように、２つの電極３３を配置し、１３０℃で５分間、３８ｋｇｆ／ｃｍ²の圧力で、ホットプレスを用いてこれらを接合し、図１０に示すようなＭＥＡ３５を得た。ここでは、水素イオン伝導性高分子電解質膜として、上記化学式（１）（ただし、ｍ＝２）で示されるパーフルオロカーボンスルホン酸からなる厚み５０μｍの膜を用いた。
【００９２】
このように作製したＭＥＡを、比較例７と同様にして、図６または図７に示すガス流路を形成した導電性セパレータ板（バイポーラ板）で上述のように両側から挟み単電池を得た。
このような単電池を２個積層した後、冷却水が流れる冷却流路を形成した導電性セパレータを冷却部として積層し、このパターンを繰り返して積層した。
この要領で合計で単電池を４０個積層した積層体を得、積層体の両端部に金属製の集電板、電気絶縁材料からなる絶縁板、および端板を配して締結ロッドで固定し、スタックを得た。このときの締結圧は導電性セパレータ板の単位面積当たり１０ｋｇｆ／ｃｍ²とした。
【００９３】
上述のようにして得たスタックに、図１１に示したマニホールドを取り付けた。図１１に示すように、スタックの上部および下部にはＳＵＳ３０４製の金属端板４１を配した。また、スタック両側面には絶縁体４２を配し、さらにガスケット４３を介してマニホールド４４および４５を取り付けた。前記マニホールド４４はアノードに水素を供給して流通させ、マニホールド４５は冷却水を供給して流通させる。また、マニホールド４６はカソードに空気を供給して流通させる。このようにして、本発明の参考例３に係る燃料電池Ａを作製した。
【００９４】
この燃料電池Ａに、燃料ガスとして純水素を７５℃に保った脱イオン水バブラーを通じて供給し、酸化剤ガスとして空気を所定温度に保った脱イオン水バブラーを通じて供給し、さらに冷却水を通じて発電試験を行った。このとき、燃料ガス、酸化剤ガスおよび冷却水ともに同一方向に導入し、ガス出口は常圧に開放した。また、冷却水量を調節して燃料電池の温度を７５℃に保ち、水素利用率７０％、酸素利用率４０％、水素加湿のバブラー温度を７５℃、空気加湿のバブラー温度を６５℃として運転し、このときの電流−電圧特性試験を行った。この結果を図１２に示した。
【００９５】
図１２には、比較のために、ガス拡散層のガーレー定数を０．５とした燃料電池Ｂと、ガス拡散層のガーレー定数を７０とした燃料電池Ｃの評価結果も合わせて示した。なお、燃料電池Ｂと燃料電池Ｃの構成は、ガス拡散層のガーレー定数以外は、燃料電池Ａと同一とした。
【００９６】
図１２において、燃料電池Ｂは導電率が比較的低いため、また、燃料電池Ｃはガス拡散性が比較的低いために、いずれも高電流密度において電池性能が若干低下していることがわかる。これに対して、燃料電池Ａは、ガス拡散性と導電率を高いレベルで両立されているために、燃料電池ＢおよびＣと比べてより優れた特性を有することがわかる。
【００９７】
また同様にして、カソード中のガス拡散層のガス透過率を、アノード中のガス拡散層のガス透過率の１．２〜２．０倍としたときも、上記参考例と同様の優れた特性が得られた。
また、カソード中のガス拡散層の気孔率を、アノード中のガス拡散層の気孔率の１．２〜２．０としたときも、上記参考例と同様の優れた特性が得られた。
【００９８】
参考例６
本参考例では、ガス拡散層を構成する導電性多孔質基材であるカーボンペーパの厚みを変更することによって、カソードのガス拡散層の厚みを、アノードのガス拡散層の厚みの１.５倍とした他は、参考例３の燃料電池Ａと同様にして燃料電池Ｄを作製した。この燃料電池Ｄでは、生成水を蒸発させなければならないカソード側で、充分な蒸発面積が確保できるため、過剰な水分を安全かつ速やかに排出することができ、濡れによる性能低下を防止できる。
【００９９】
この燃料電池Ｄに関して、参考例３と同じ条件で電流−電圧特性の評価試験を行った。その結果を図１３に示す。図１３において、本実施例の燃料電池Ｄも参考例３の燃料電池Ａと、ほぼ同等の電池特性を有することがわかった。
【０１００】
参考例７
参考例３〜６において作製した燃料電池においては、ガス拡散層のガーレー定数は、ＭＥＡおよびスタック作製の際の加圧圧力の影響を受ける。参考例３の燃料電池Ａの作製工程では、ホットプレスでＭＥＡを作製する際に、加圧力を調整し、プレス後のガス拡散層の厚みをプレス前のガス拡散層の厚みの７５〜９０％とした。
【０１０１】
燃料電池Ｅ、ＦおよびＧを、ＭＥＡのホットプレス時の圧力をそれぞれ３５、２０および５０ｋｇｆ／ｃｍ²とした他は、実施例８に係る燃料電池Ａと同様にして作製した。本実施例では、このように、ＭＥＡのホットプレス時の圧力を変えて、この影響を評価し、結果を図１４に示した。
【０１０２】
図１４からわかるように、圧力を大きくしすぎた燃料電池Ｇは、燃料電池Ｅの約７０％の厚みとなり、ガス拡散層が座屈し、ガス透過性が極端に低下するため、高電流密度域での特性が低下してしまった。また、加圧力が小さい燃料電池Ｆは、燃料電池Ｅの約１３０％の厚みとなり、接触抵抗が大きくなるため、全体的に電圧が低下した。
【０１０３】
参考例８
本参考例では、参考例３のスタックにおいて、電極面積をさらに大型化し、導電性セパレータ板に設けられたガス流路のパターンに沿って、リブに接する部分のガス拡散層を薄く密にし、ガス流路部分に当たる部分のガス拡散層を厚く粗にした。ガス拡散層の密な部分の厚みは、粗な部分の厚みの７０〜９５％とした他は、実施例８に係る燃料電池Ａと同様にして燃料電池Ｈを得た。
【０１０４】
燃料電池Ｈでは、ガス流路を流れてきたガスがガス拡散層を通って触媒層に達する。ここで、リブに接する部分のガス拡散層のガス透過性が高いと、ガス拡散層のその部分を介して隣接するガス流路間をガス移動してしまい、ガス流路に沿ってガスをＭＥＡの隅々にまで供給できないことになる。特に、電極の面積を大きくするにしたがって、ガスをＭＥＡの隅々にまで供給しにくくなる。逆に、ガス透過性が低いと、リブに対応する部分に位置する触媒層へのガスの供給が不充分となり、電池性能が低下する原因となる。このため、リブに接触する部分のガス拡散層は、ガス透過性が適度に低下していることが必要である。
【０１０５】
また、ガス拡散層は、反応によって発生した電子を集める役割を果たし、ガス流路部分で発生した電子をリブ部分にまで運搬する。このため、ガス拡散層の厚い部分と薄い部分の密度を同様とした場合は、ガス流路部分に位置するガス拡散層を厚くし、その断面積を大きくする方が導電性の面で有利となる。
この燃料電池Ｇに関して、参考例３と同じ条件で電流―電圧特性評価試験を行った。その結果を図１５に示す。図１５から、大きい電極面積を有する本参考例の燃料電池Ｈは、参考例３の燃料電池Ａとほぼ同等の電池特性を有することがわかる。
【０１０６】
産業上の利用の可能性
上述のように、本発明によれば、アノードおよびカソードの撥水性の程度を位置によって変化させることにより、高い放電特性、特に高電流密度域で高い電流−電圧特性を有する優れた高分子電解質型燃料電池を得ることができる。また、本発明によれば、アノードおよびカソードを構成するガス拡散層における炭素粉末の撥水性、比表面積、一次粒子径およびＤＢＰ吸油量などを最適化することによって、高い放電性能を有する優れた高分子電解質型燃料電池を得ることができる。
【図面の簡単な説明】
【図１】 導電性多孔質基材にスプレー塗布を施すために用いる塗布装置の構成図である。
【図２】 本発明の参考例および比較例において得られた単電池の電流−電圧特性を示すグラフである。
【図３】 導電性多孔質基材にスプレー塗布を施すために用いる別の塗布装置の構成図である。
【図４】 本発明の参考例および比較例において得られた単電池の電流−電圧特性を示すグラフである。
【図５】 本発明の実施例において作製したＭＥＡの概略縦断面図である。
【図６】 表面にガス流路（溝）を形成した導電性セパレータ板の概略平面図である。
【図７】 表面にガス流路（溝）を形成した別の導電性セパレータ板の概略平面図である。
【図８】 本発明の実施例および比較例において作製した燃料電池の放電特性を示すグラフである。
【図９】 本発明の実施例および比較例において作製した燃料電池の放電特性を示すグラフである。
【図１０】 本発明の実施例および比較例において作製したＭＥＡの概略縦断面図である。
【図１１】 本発明の実施例において作製した燃料電池の概略斜視図である。
【図１２】 本発明の実施例および比較例において作製した燃料電池の放電特性を示すグラフである。
【図１３】 本発明の実施例および比較例において作製した燃料電池の放電特性を示すグラフである。
【図１４】 本発明の実施例および比較例において作製した燃料電池の放電特性を示すグラフである。
【図１５】 本発明の実施例および比較例において作製した燃料電池の放電特性を示すグラフである。[0001]
Technical field
  The present invention relates to a room temperature operation type polymer electrolyte fuel cell used for portable power supplies, electric vehicle power supplies, domestic cogeneration systems, and the like.
[0002]
Background art
  A polymer electrolyte fuel cell generates electricity and heat simultaneously by electrochemically reacting a fuel gas containing hydrogen and an oxidant gas containing oxygen such as air.
[0003]
  In order to obtain this fuel cell, first, a catalyst layer mainly composed of carbon powder carrying a platinum-based metal catalyst is formed on both surfaces of a polymer electrolyte membrane that selectively transports hydrogen ions. Next, a gas diffusion layer having both air permeability and electron conductivity with respect to the fuel gas or oxidant gas is formed on the outer surface of the catalyst layer, and the catalyst layer and the gas diffusion layer are combined to form an electrode. This assembly of the electrode and the electrolyte membrane is called MEA.
[0004]
  Next, a gasket is disposed around the electrode with a polymer electrolyte membrane interposed so that the supplied gas does not leak out or the fuel gas and the oxidant gas are mixed with each other. In some cases, an MEA in which the gasket, the electrode, and the polymer electrolyte membrane are integrated and assembled in advance is obtained.
[0005]
  A conductive separator plate for mechanically fixing the MEAs and electrically connecting adjacent MEAs to each other in series is disposed outside the MEA. In the portion of the separator plate that contacts the MEA, a reaction gas is supplied to the electrode surface, and a gas flow path for carrying away the generated gas and surplus gas is formed. Although the gas flow path can be separately provided in the separator plate, generally, the gas flow path is formed by forming a groove on the surface of the separator plate.
[0006]
  In addition, since the conductive separator plate is required to have high electron conductivity, gas tightness, and high corrosion resistance, conventionally, a conductive separator plate is formed by forming grooves on a dense carbon plate by a processing method such as cutting. I was getting.
[0007]
  The gas flow path provided in the conventional conductive separator plate is generally provided with a plurality of gas flow paths (straight type flow paths) in parallel from the gas inlet to the gas outlet. there were. However, in the polymer electrolyte fuel cell, there is a problem that generated water is generated on the cathode side during operation, and the cell performance cannot be sufficiently exhibited unless the generated water is efficiently removed. Therefore, the length per gas channel is increased by reducing the cross-sectional area of the gas channel provided in the conductive separator plate and meandering the gas channel (serpentine type channel). Yes. Thereby, the gas flow rate can be substantially increased, the generated water can be forcibly removed, and the battery performance can be improved.
[0008]
  Normally, when a fuel cell is actually used, a stacked battery structure is formed by laminating several unit cells described above. Since heat is generated together with electric power during operation of the fuel cell, in the laminated battery, a cooling plate is provided for each unit cell, and the generated thermal energy is used for hot water etc. at the same time as keeping the battery temperature constant. .
[0009]
  As a general cooling plate, a thin metal plate having a structure through which a heat medium such as cooling water flows is used. However, the conductive separator plate can also be used as a cooling plate by forming a flow path on the back surface of the conductive separator plate constituting the unit cell, that is, the surface of the conductive separator plate where the cooling water is to flow. At that time, an O-ring and a gasket for sealing a heat medium such as cooling water are also required. In this case, it is necessary to ensure sufficient conductivity between the upper and lower sides of the cooling plate by completely crushing the O-ring.
[0010]
  In such a stacked battery, a supply / discharge hole for fuel gas and oxidant gas to each unit cell called a manifold is required. In particular, a so-called internal manifold in which cooling water supply and discharge holes are secured inside the laminated battery is generally used.
  Regardless of whether the internal manifold or the external manifold is used, a plurality of single cells including a cooling unit are stacked in one direction to obtain a laminated body (laminated battery), and a pair of end plates are arranged at both ends of the laminated body. It is necessary to fix between the two end plates with a fastening rod.
[0011]
  When fastening using a fastening rod, it is desirable to fasten the cells as uniformly as possible in the surface direction. From the viewpoint of mechanical strength, a metal material such as stainless steel is usually used for the end plate and the fastening rod. These end plates and fastening rods and the laminate are electrically insulated by an insulating plate, and form a structure in which current does not leak outside through the end plate. The fastening rod can be passed through a through-hole in the separator, and a method of fastening the entire laminate with a metal belt over an end plate has been proposed.
[0012]
  The polymer electrolyte fuel cell obtained as described above functions as an electrolyte in a state in which the electrolyte membrane contains moisture, so it is necessary to supply fuel gas and oxidant gas with humidification. In addition, in the temperature range up to at least 100 ° C., the higher the water content of the polymer electrolyte membrane, the higher the ion conductivity, the lower the internal resistance of the battery, and the higher the performance.
[0013]
  However, if highly humidified gas at a temperature higher than the battery operating temperature is supplied, condensed water is generated inside the battery, and water droplets hinder smooth gas supply. At the same time, since water is generated by power generation on the cathode side where the oxidant gas is supplied, there arises a problem that the efficiency of removing the generated water is lowered and the battery performance is lowered. For this reason, the gas is usually supplied after being humidified so as to have a dew point slightly lower than the battery operating temperature.
[0014]
  Common supply gas humidification methods include a bubbler humidification method in which supply gas is bubbled and humidified in deionized water maintained at a predetermined temperature, and one surface of a membrane such as an electrolyte membrane that allows easy movement of moisture. There is a membrane humidification method in which deionized water maintained at a predetermined temperature is supplied and a supply gas is supplied to the other surface for humidification. When a gas obtained by steam reforming a fossil fuel such as methanol or methane is used as the fuel gas, humidification may not be necessary because the reformed gas contains steam.
[0015]
  The humidified fuel gas and oxidant gas are supplied to the polymer electrolyte fuel cell for power generation. At this time, a current density distribution is generated in a single plane of any single cell in the laminated battery. That is, the fuel gas is humidified and then supplied into the fuel cell through the gas supply port, but hydrogen in the fuel gas is consumed by power generation. Therefore, a phenomenon occurs in which the hydrogen partial pressure is higher and the water vapor partial pressure is lower in the upstream part of the gas flow path, and the hydrogen partial pressure is lower and the water vapor partial pressure is higher in the downstream part of the gas flow path.
[0016]
  The oxidant gas is also humidified and then supplied into the fuel cell through the gas supply port. However, oxygen in the oxidant gas is consumed by power generation, and water generated by power generation is generated. Therefore, a phenomenon occurs in which the oxygen partial pressure is higher and the water vapor partial pressure is lower in the upstream part of the gas flow path, and the oxygen partial pressure is lower and the water vapor partial pressure is higher in the downstream part of the gas flow path.
  Furthermore, since the cooling water temperature for cooling the battery is lower at the entrance and higher at the exit, a temperature distribution is generated in a single surface of the battery. For the reasons described above, a current density distribution (performance distribution) occurs in a single plane of the battery.
[0017]
  In addition, the hydrogen partial pressure and water vapor partial pressure non-uniformity in the fuel gas within the single surface of the battery as described above, the oxygen partial pressure and water vapor partial pressure non-uniformity in the oxidant gas, and the temperature distribution, etc. However, when it becomes extremely large and deviates from the optimum state, it leads to an extremely dry state (over dry) or an extremely wet state (over flooding). Furthermore, a phenomenon may occur in which an overdry state and an overflooding state coexist in a single surface of the battery. If it does so, there will also be a problem that it does not function only by generation | occurrence | production of electric current density distribution, and it stops functioning depending on the case.
[0018]
  When the number of unit cells included in the stacked battery is large, when the above-described problem occurs in some of the unit cells of the stacked unit cells, the stacked battery is used for some of the unit cells whose performance has deteriorated. It will interfere with the overall driving. That is, when a part of single cells of the laminated battery falls into an overflooding state, the pressure loss for gas supply increases in the single cell. Since the gas supply manifold is connected to each unit cell in the stacked cell, if one unit cell falls into the overflooding state, it becomes difficult for the gas to flow, and another unit cell also overfloods. As more and more overflooding is promoted.
[0019]
  On the contrary, when some of the unit cells of the laminated battery fall into an overdry state, the pressure loss for gas supply decreases in the unit cell. Therefore, gas easily flows into the unit cell that has fallen into the overdry state, and as a result, the overdry state is further promoted.
  The above-described problem is that the partial pressure of water vapor in the gas is higher on the gas outlet side than on the gas supply port side on both the anode side supplying the fuel gas and the cathode side supplying the oxidant gas. Often due to
[0020]
  When a polymer electrolyte fuel cell is used as a power source for an electric vehicle, compactness, weight reduction and cost reduction are strongly demanded, and response at high output, that is, high in a high current density region, is required. Current-voltage characteristics are required. Therefore, it is desirable to avoid the overflooding state and the overdrying state as described above.
  By the way, the electrode (anode and cathode) of a polymer electrolyte fuel cell is generally composed of a catalyst layer formed on both surfaces of the polymer electrolyte membrane and a gas diffusion layer formed on the outer surface of the catalyst layer. The gas diffusion layer mainly has the following three functions.
[0021]
  The first function is a function of diffusing the gas so that the fuel gas or the oxidant gas is uniformly supplied from the gas flow channel located on the outer surface of the gas diffusion layer to the catalyst in the catalyst layer. The second function is a function for quickly discharging generated water generated in the catalyst layer to the gas flow path. The third function is a function of conducting electrons required for the reaction or generated electrons.
[0022]
  Accordingly, the gas diffusion layer requires high reaction gas permeability, water vapor permeability, and electronic conductivity. As a conventional technique, a gas diffusion layer has a porous structure in order to increase gas permeability, a water repellent polymer such as a fluororesin is dispersed in the gas diffusion layer in order to increase water vapor permeability, and electrons In order to enhance the conductivity, a method of forming a gas diffusion layer with an electron conductive material such as carbon fiber, metal fiber, or carbon powder has been adopted.
[0023]
  However, the above methods for improving gas permeability, water vapor permeability, and electronic conductivity each show contradictory effects. For example, when the porosity of the gas diffusion layer is increased by reducing the diameter of the carbon fibers or reducing the filling amount in order to increase the gas permeability, the electron conductivity is lowered. In addition, when a water-repellent polymer is added to increase water vapor permeability, gas permeability and electronic conductivity are lowered.
  Therefore, instead of constituting the gas diffusion layer with a single member, for example, a layer made of carbon fiber and a layer made of carbon powder and a water-repellent polymer are combined, and efforts have been made to successfully balance the contradictory functions. Yes. However, there is no prior art in which the above-mentioned carbon powder defines in detail the various properties required as a gas diffusion layer and has demonstrated it.
[0024]
  In addition, an electrode obtained by disposing carbon powder supporting a noble metal as a catalyst on a conductive porous substrate constituting a gas diffusion layer is generally obtained by using carbon powder supporting a noble metal as an organic material such as isopropyl alcohol. An ink is obtained by mixing with a solvent, and the ink is formed on a substrate using a screen printing method or a transfer method. There is also a method in which a slurry containing catalyst powder is prepared and this slurry is applied on a resin sheet using a doctor blade method or the like.
  In these electrodes, carbon powder or the like carrying polytetrafluoroethylene (PTFE) is mixed in the ink to increase the water repellency of the electrode.
[0025]
  In order to reduce deterioration of characteristics due to current distribution in the electrode surface, it is effective to change the water repellency configuration of the electrode in the electrode surface direction or gas diffusion (thickness) direction. In particular, in the vicinity of the outlet of the gas flow path of the electrode, the pressure of the supply gas is lower than in the vicinity of the inlet, and the relative humidity tends to decrease and dry, and the water retention inside the MEA is increased from the inlet to the outlet. Is preferred.
  However, conventional electrode printing methods such as the screen printing method and doctor blade method cannot change the electrode configuration in the surface direction, and require repeated coating in the thickness direction, which complicates the manufacturing process. There is a problem of becoming.
[0026]
  From the above, the present invention firstly has a high discharge characteristic, particularly a high current density, by changing the degree of water repellency of the anode and the cathode depending on the position in order to solve the conventional problems as described above. An object of the present invention is to provide an excellent polymer electrolyte fuel cell having high current-voltage characteristics in the region. The present invention also provides an excellent polymer electrolyte fuel cell having high discharge performance, particularly by optimizing the water repellency, specific surface area, primary particle size, DBP oil absorption amount and the like of carbon powder at the anode and cathode. The purpose is to provide.
[0027]
Disclosure of the invention
  The present invention provides a pair of conductive materials in which a cathode and an anode stacked at a position sandwiching a hydrogen ion conductive polymer electrolyte membrane are formed, and a gas flow path for supplying an oxidant gas and a fuel gas to the cathode and the anode, respectively. A polymer electrolyte fuel cell including a single cell sandwiched between separator plates, wherein the cathode and anode are composed of catalyst particles, a hydrogen ion conductive polymer electrolyte, a conductive porous substrate, and a water repellent. The water repellency of the cathode is higher than the water repellency of the anode.In addition, the cathode and the anode have a catalyst layer bonded to the hydrogen ion conductive polymer electrolyte membrane, and a gas diffusion layer in contact with the conductive separator plate, and the catalyst layer is supported on carbon particles. And the hydrogen ion conductive polymer electrolyte, the gas diffusion layer is made of a conductive porous substrate containing carbon particles, and the water repellency of the carbon particles contained in the gas diffusion layer is included in the catalyst layer. It is higher than the water repellency of the carbon particles, and the water repellency of at least one of the cathode and the anode varies with respect to the thickness direction, and the carbon particles contained in the gas diffusion layer include the catalyst layer and the conductive porous group. Placed at the joint with the materialThe present invention relates to a polymer electrolyte fuel cell.
[0028]
  In this case, it is effective that the gas permeability of the conductive porous substrate is 1 to 60 seconds / 100 mL in terms of Gurley constant.
  In addition, it is effective that the gas permeability of the conductive porous substrate in the cathode is 1.2 to 2.0 times the gas permeability of the conductive porous substrate in the anode.
  In addition, it is effective that the porosity of the conductive porous substrate in the cathode is 1.2 to 2.0 times the porosity of the conductive porous substrate in the anode.
  In addition, it is effective that the thickness of the conductive porous substrate in the cathode is 1.2 to 3.0 times the thickness of the conductive porous substrate in the anode.
[0030]
  MaIn addition, it is effective that the specific surface area of the carbon particles contained in the gas diffusion layer is ½ or less of the specific surface area of the carbon particles contained in the catalyst layer.
  In addition, it is effective that the primary particle size of the carbon particles contained in the gas diffusion layer is 1.3 times or more the primary particle size of the carbon particles contained in the catalyst layer.
  Further, it is effective that the DBP oil absorption amount of the carbon particles contained in the gas diffusion layer is 2/3 or less of the DBP oil absorption amount of the carbon particles contained in the catalyst layer.
[0031]
BEST MODE FOR CARRYING OUT THE INVENTION
  The present invention provides a polymer electrolyte fuel cell in which the water and water repellency distributions of the anode and the cathode are controlled to smoothly move the gas, moisture, and the like inside the fuel cell, so that the cell performance is hardly deteriorated. Therefore, the present invention can take various embodiments under such a concept.
[0032]
  In the present invention, a cathode and an anode laminated at positions sandwiching a hydrogen ion conductive polymer electrolyte membrane are respectively connected to the cathode and the anode.OxidantA polymer electrolyte fuel cell including a single cell sandwiched between a pair of conductive separator plates in which a gas flow path for supplying gas and fuel gas is formed, wherein the cathode and anode are catalyst particles, hydrogen It consists of an ion conductive polymer electrolyte, a conductive porous substrate and a water repellent,The water repellency of the cathode is higher than the water repellency of the anode.This is a polymer electrolyte fuel cell.
[0033]
  That is, the polymer electrolyte fuel cell of the present invention is a conductive separator having a hydrogen ion conductive polymer electrolyte membrane, a pair of electrodes (anode and cathode) sandwiching the membrane, and a flow path for supplying gas to each electrode. A plate is provided.
  Here, the electrode may include a conductive porous substrate forming a gas diffusion layer, and a porous catalyst layer formed between the substrate and a hydrogen ion conductive polymer electrolyte membrane. A conductive fine particle (for example, carbon powder) layer may be formed between the conductive porous substrate and the catalyst layer.
[0034]
  Further, in the fuel cell according to the present invention, the cathode and the anode have a catalyst layer bonded to the hydrogen ion conductive polymer electrolyte membrane, and a gas diffusion layer in contact with the conductive separator plate, The layer is composed of catalyst particles supported on carbon particles and a hydrogen ion conductive polymer electrolyte, the gas diffusion layer is composed of a conductive porous substrate containing carbon particles, and the repellent properties of the carbon particles contained in the gas diffusion layer. It is preferable that the aqueous property is higher than the water repellency of the carbon particles contained in the catalyst layer, and the water repellency of at least one of the cathode and the anode varies in the thickness direction. For example, in the electrode, it is effective that the water repellency of the carbon particles arranged in the gas diffusion layer is higher than the water repellency of the carbon particles arranged in the catalyst layer. Thereby, in the polymer electrolyte fuel cell of the present invention, there is an advantage that the reaction gas can be uniformly supplied to the catalyst of the catalyst layer and the generated water can be quickly discharged.
[0035]
  As described above, the water repellency inclined in the direction along the gas flow path or in the direction opposite to the gas diffusion direction (surface direction or thickness direction) is repelled from the spray nozzle that can scan two-dimensionally at an arbitrary speed. A hydrogen ion conductive polymer electrolyte membrane, a catalyst layer, a conductive fine particle layer, or a conductive porous substrate, which is a surface to be adhered (coated surface) alone or together with a dispersion of liquid medicine, together with catalyst particles or conductive fine particles It can be realized by a process of applying on top.
  According to the said process, most of a solvent can be evaporated before each dispersion liquid adheres on a to-be-coated surface, and a to-be-coated surface is not swollen with a solvent.
[0036]
  Further, in the above step, since the spray nozzle can be scanned two-dimensionally at an arbitrary speed, the scanning speed is continuously increased or decreased, and the dispersion of the water repellent agent is sprayed from the spray nozzle. The spray nozzle can be scanned along the direction from the inlet of the gas flow path to the outlet or from the outlet to the inlet while being applied on the conductive porous substrate or the conductive fine particle layer. At this time, the lower the scanning speed of the spray nozzle, the greater the amount of water repellent per unit area that is adhered by spray coating.
[0037]
  In addition, a spray nozzle for injecting a dispersion of catalyst particles or conductive fine particles and a spray nozzle for injecting a dispersion of a water repellent agent are arranged in the vicinity, and at the same time, the gas flow path inlet to the outlet or outlet to the inlet It is also possible to scan along the direction toward. At this time, the spraying speed of the dispersion liquid of catalyst particles or conductive fine particles is kept constant, and only the spraying speed of the dispersion liquid of the water repellent is continuously increased or decreased from the two spray nozzles to the polymer electrolyte membrane or When each dispersion liquid is simultaneously spray-coated on the conductive porous substrate, the amount of the water-repellent agent per unit area deposited by spray coating increases in the scanning portion where the spray speed of the water-repellent agent is large.
[0038]
  Also, once the catalyst particle or conductive fine particle dispersion and the water repellent dispersion are sent to the mixing container, the mixed dispersion is sequentially sent to the spray nozzle, and the spray nozzle is introduced from the inlet of the gas flow path. Spray application can also be performed while scanning from the outlet or from the outlet to the inlet. At this time, if the content ratio of the water repellent in the mixed dispersion is changed over time, the amount of the water repellent per unit area adhered by spray coating in the scanning portion where the content ratio of the water repellent is large. Will increase.
  Therefore, according to the said process, the catalyst layer, the electroconductive porous base material, and the electroconductive fine particle layer which have the water repellency inclined in the direction along the flow path of gas can be produced easily.
[0039]
  Further, once the catalyst particle or conductive fine particle dispersion and the water repellent dispersion are sent to the mixing container, the mixed dispersion is sequentially sent to the spray nozzle, and the position of the spray nozzle is fixed, The dispersion can also be spray-coated on a polymer electrolyte membrane or a conductive porous electrode substrate. When the content ratio of the water repellent in the mixed dispersion at this time is changed over time, a catalyst layer or conductive fine particle layer having water repellency that is inclined in the gas diffusion direction (thickness direction) is formed. You can also. Further, such a catalyst layer or conductive fine particle layer can also be prepared by repeatedly applying the water-repellent agent in the dispersion liquid while changing the content ratio.
[0040]
  What is necessary is just to select suitably the conditions at the time of spray-coating each dispersion liquid according to the kind of solvent, the kind of water repellent. In particular, nozzle hole diameter 0.5-2mm, atomization pressure (injection pressure from nozzle) 0.5-3kgf / cm²The nozzle height (distance between the nozzle and the adherend surface) is preferably 5 to 30 cm. Moreover, the preferable average particle diameter of the microparticles | fine-particles contained in the discharged dispersion liquid is 0.1-20 micrometers.
  Moreover, the preferable content rate of solid content in each dispersion liquid is 5 to 20 weight%, and a preferable viscosity is 50 P or less.
[0041]
  As the hydrogen ion conductive polymer electrolyte membrane, a membrane made of perfluorocarbon sulfonic acid represented by Nafion membrane manufactured by Du Pont, USA, a hydrocarbon membrane manufactured by Hoechst, etc. can be preferably used. As the conductive porous substrate, carbon paper, carbon cloth, carbon-PTFE composite sheet (one obtained by kneading carbon and PTFE) and the like can be preferably used. As the water repellent, a fluororesin such as PTFE can be preferably used.
[0042]
  As the catalyst particles, carbon powder having an average particle diameter of 100 to 1000 nm and supporting a noble metal can be preferably used. The dispersion of catalyst particles may contain a polymer electrolyte, carbon powder that has been subjected to a water repellent treatment with a fluororesin, a water repellent, and the like.
  The conductive fine particle layer is desirably composed of a carbon material, a metal material, a carbon-polymer composite material, a metal-polymer composite material, or the like having an average particle diameter of 0.1 to 10 μm. Among these, as the carbon-polymer composite material, carbon powder to which a fluorine-based resin is attached is desirable. The dispersion of conductive fine particles may contain a polymer electrolyte, a water repellent and the like.
[0043]
  As the solvent, for example, ethanol, isopropanol, butanol, ethoxyethanol, pentyl alcohol, butyl acetate, water and the like can be preferably used. These may be used alone or in combination of two or more. Among these, ethanol, butanol and butyl acetate are particularly preferable because they are easily vaporized by injection.
  As the conductive separator plate formed with a flow path for supplying gas to each electrode used in the present invention, those conventionally used in general can be used without any particular limitation. Further, there is no particular limitation on the shape of the polymer electrolyte fuel cell including a unit cell obtained by laminating the electrode and the separator plate.
[0044]
  BookA cathode and an anode disposed at a position sandwiching the hydrogen ion conductive polymer electrolyte membrane according to the invention, and a pair of conductive materials forming a gas flow path for supplying an oxidant gas and a fuel gas to the cathode and the anode, respectively. In a polymer electrolyte fuel cell including a single cell sandwiched between conductive separator plates, the following configuration is preferably used.
[0045]
  The cathode and the anode include a catalyst layer bonded to the hydrogen ion conductive polymer electrolyte membrane, and a gas diffusion layer in contact with the conductive separator plate. The catalyst layer is supported on carbon particles. It is made of a hydrogen ion conductive polymer electrolyte, the gas diffusion layer is formed by disposing carbon particles on a conductive porous substrate, and the water repellency of the carbon particles disposed in the gas diffusion layer of the cathode is the gas of the anode. It is effective that it is higher than the water repellency of the carbon particles arranged in the diffusion layer. Accordingly, there is an advantage that flooding of the gas diffusion layer due to generated water at the cathode is suppressed, and an appropriate amount of water is confined by water repellency of the gas diffusion layer, thereby enhancing the water retention effect of the cathode catalyst layer.
[0046]
  The gas diffusion layer is preferably made of a conductive porous substrate, and carbon particles are preferably dispersed in the conductive porous substrate.
  Furthermore, in the polymer electrolyte fuel cell according to the present invention, it is effective that the gas permeability of the conductive porous substrate is 1 to 60 seconds / 100 mL in terms of Gurley constant. As a result, when the conductive porous substrate that constitutes the gas diffusion layer is properly densified, a polymer electrolyte fuel cell that achieves both electrode conductivity and gas diffusibility and has a small voltage drop even with a large driving current is realized. can do.
[0047]
  In addition, it is effective that the gas permeability of the conductive porous substrate in the cathode is 1.2 to 2.0 times the gas permeability of the conductive porous substrate in the anode. Thereby, compared with fuel gas, for example, even when air having a low oxygen concentration is used as the oxidant gas, there is an advantage that the supply amount of the oxidant gas to the catalyst layer is not insufficient. If it is smaller than 1.2, it causes a voltage drop due to insufficient oxygen supply in the high current density region, and if it is larger than 2.0, the porosity becomes excessively high to ensure high gas permeability, and the electrode strength decreases. There are disadvantages such as low electrical conductivity.
[0048]
  Further, it is effective that the porosity of the conductive porous substrate in the cathode is 1.2 to 2.0 times the porosity of the conductive porous substrate in the anode. There is an effect similar to the gas permeability.
  In addition, it is effective that the thickness of the conductive porous substrate in the cathode is 1.2 to 3.0 times the thickness of the conductive porous substrate in the anode. Thereby, there exists an advantage that the layer for controlling water repellency and water retention can fully be ensured. Outside this range, there is a disadvantage that gas permeability, conductivity, and water repellency are lowered.
[0049]
  Further, the carbon particles contained in the gas diffusion layer may contain the catalyst layer and the conductive porous group.MaterialIt is effective to be arranged at the joint portion. For example, the catalyst layer and the gas diffusion layer are joined by forming a layer in which the carbon powder arranged in the gas diffusion layer and the carbon powder arranged in the catalyst layer are mixed at the interface between the catalyst layer and the gas diffusion layer. The area increases. And there exists an effect that reaction gas, generated water, and an electron move quickly efficiently, and battery performance improves.
[0050]
  In addition, it is effective that the specific surface area of the carbon particles contained in the gas diffusion layer is ½ or less of the specific surface area of the carbon particles contained in the catalyst layer. Carbon powder with a small specific surface area has lower water absorption and higher water repellency than carbon powder with a large specific surface area. Therefore, the water repellency of the carbon powder of the gas diffusion layer can be made higher than that of the catalyst layer by setting the specific surface area of the carbon powder of the gas diffusion layer to ½ or less of the specific surface area of the carbon powder of the catalyst layer.
[0051]
  Here, it is also effective to set the specific surface area of the carbon powder used for the cathode-side gas diffusion layer to ½ or less of the specific surface area of the carbon powder used for the anode-side gas diffusion layer. As a result, the generated water can be discharged quickly, and the gas diffusion capacity of the cathode can be improved.
[0052]
  In addition, it is effective that the primary particle size of the carbon particles contained in the gas diffusion layer is 1.3 times or more the primary particle size of the carbon particles contained in the catalyst layer. The smaller the primary particle size of the carbon powder, the larger the specific surface area and the lower the water repellency. Therefore, the water repellency of the gas diffusion layer can be made higher than the water repellency of the catalyst layer by making the particle size of the carbon particles of the gas diffusion layer 30% or more larger than the particle size of the carbon particles of the catalyst layer.
[0053]
  Here, by making the particle size of the primary particles of the carbon particles used for the gas diffusion layer on the cathode side 30% or more larger than the particle size of the primary particles of the carbon particles used for the gas diffusion layer on the anode side, It becomes possible to discharge quickly, and the gas diffusion capacity of the cathode can be improved.
[0054]
  In addition, it is effective that the DBP oil absorption amount of the carbon particles contained in the gas diffusion layer is 2/3 or less of the DBP oil absorption amount of the carbon particles contained in the catalyst layer. A carbon particle having a larger DBP oil absorption defined by the carbon black test method for rubber (JIS K 6221) has a more developed structure and a higher porosity. When carbon particles having a well-developed structure are used, the specific surface area is large and moisture is easily adsorbed and wettable. Therefore, by making the DBP oil absorption amount of the carbon particles of the gas diffusion layer 2/3 or less than the DBP oil absorption amount of the carbon particles of the catalyst layer, the water repellency of the gas diffusion layer can be increased and the gas diffusion ability can be improved. it can.
[0055]
  Here, the water repellency of the gas diffusion layer is reduced by setting the DBP oil absorption amount of the carbon particles used for the gas diffusion layer on the cathode side to 2/3 or less of the DBP oil absorption amount of the carbon particles used for the gas diffusion layer on the anode side. The gas diffusion capacity can be improved by increasing.
  Hereinafter, the present invention will be described using examples, but the present invention is not limited to these examples.
[0056]
referenceExample 1
  A gas diffusion layer having water repellency inclined in a direction along the gas flow path using a carbon paper (manufactured by Toray Industries, Inc.) having a film thickness of 360 μm as the spray coating apparatus and the conductive porous substrate shown in FIG. Was prepared.
[0057]
  In FIG. 1, a dispersion liquid of polytetrafluoroethylene (ND-1 manufactured by Daikin Industries, Ltd.) was placed in a container 1 and constantly stirred with a stirring blade. The dispersion in the container 1 was pressed into the spray nozzle 3 by the pump 2. The solution not sprayed from the spray nozzle 3 was circulated and collected in the container 1. The spray nozzle 3 was able to scan two-dimensionally at an arbitrary speed by two actuators.
[0058]
  A mask frame 5 cut to a size of 60 mm × 60 mm was placed on the carbon paper 4, and the spray nozzle 3 was moved while spraying the dispersion with the spray nozzle 3 from above. At that time, the spray nozzle 3 was moved while continuously increasing the scanning speed along the direction from the outlet to the inlet of the gas flow path when the unit cells were assembled.
  The carbon paper was cut in a direction along the gas flow path, a small piece was sampled, and the weight was measured. The amount of fluororesin added to the carbon paper from the inlet to the outlet of the gas flow path was in the range of 0 to 50% by weight. It was found that it increased continuously.
[0059]
  Thereafter, the carbon paper (gas diffusion layer) after the water repellent treatment was baked in order to remove the remaining solvent, surfactant and the like. Subsequently, a catalyst particle dispersion was screen printed on the gas diffusion layer to form a catalyst layer, thereby obtaining an electrode. Here, a 100 mesh screen was used.
[0060]
  Here, the dispersion of the catalyst particles is 20 g of 25 wt% platinum-supported carbon powder (average particle size 100 to 500 nm), 225 g of a perfluorocarbon sulfonic acid dispersion (Nafion solution manufactured by Aldrich, USA, solid content 5 wt%). In addition, 250 g of butanol as a solvent and several drops of a commercially available surfactant (NP-10 manufactured by Nippon Surfactant Kogyo Co., Ltd.) were mixed and prepared by a ball mill method.
[0061]
  After screen printing, the electrode was sufficiently dried at 80 ° C. to remove the solvent, and then a single cell was obtained by sandwiching a polymer electrolyte membrane (Nafion 112 manufactured by DuPont, USA) between the two electrodes. This single cell was set in a current-voltage characteristic measuring device for the single cell, hydrogen gas was allowed to flow through the anode (fuel electrode), and air was allowed to flow through the cathode (air electrode). The cell temperature was set to 80 ° C., the fuel utilization rate was set to 90%, and the air utilization rate was set to 30%. The hydrogen gas was humidified so that the dew point was 75 ° C. and the air was 65 ° C. The current-voltage characteristics of the obtained battery are shown in FIG.
[0062]
Comparative Examples 1-3
  Carbon paper was immersed in the above-mentioned ND-1 dispersion, and the carbon paper was heated, whereby the amount of fluororesin added in the carbon paper surface was made uniform, and the water repellent treatment of the carbon paper was performed. By adjusting the degree of dilution of the ND-1 dispersion, gas diffusion layers having a fluororesin addition amount of 0% by weight (untreated), 25% by weight, and 50% by weight, respectively, were produced. Except for using these three types of gas diffusion layers,referenceThe same operation as in Example 1 was performed. The current-voltage characteristics of the obtained battery are shown in FIG.
[0063]
  From FIG. 2, even when compared with the batteries of Comparative Examples 1 to 3 in which the fluororesin addition amount in the carbon paper surface is uniform, the fluororesin addition amount in the carbon paper surface is continuous from the inlet to the outlet of the gas flow path. Has increased toreferenceIt can be seen that the characteristics of the battery of Example 1 are superior. This indicates that it is effective for improving the battery characteristics to not only change the total addition amount of the fluororesin but also to give a continuous gradient to the addition amount of the fluororesin in the carbon paper surface. Here, the fluororesin addition amount in the carbon paper surface was changed in the range of 0 to 50% by weight. However, even when this addition amount was changed in accordance with the operating conditions of the battery, the same effect was observed if the fluorine resin addition amount was continuously increased from the inlet to the outlet of the gas flow path.
[0064]
referenceExample 2
  The spray coating apparatus shown in FIG. 3 contains ND-1 dispersion, conductive fine particle dispersion (100 g Denka Black manufactured by Denki Kagaku Kogyo Co., Ltd., 900 g water, and 2 g surfactant Triton X-100. ) And carbon paper, and a carbon layer which is a conductive fine particle layer was produced on the carbon paper constituting the gas diffusion layer.
[0065]
  The ND-1 dispersion liquid was placed in the container 6 and the carbon dispersion liquid was placed in the container 7, and each was constantly stirred with stirring blades. The ND-1 dispersion in the container 6 was pressed into the spray nozzle 9 using the pump 8, and the carbon dispersion in the container 7 was pressed into the spray nozzle 3 using the pump 10. Further, the ND-1 dispersion and the carbon dispersion which were not used were circulated and collected in a container. The spray nozzles 3 and 9 were installed very close to each other, and each of the two actuators allowed two-dimensional scanning at an arbitrary speed.
[0066]
  A mask frame 5 cut to a size of 60 mm × 60 mm was disposed on the carbon paper 4. From above, the spray nozzles 3 and 9 were moved while spraying (particulates) the ND-1 dispersion and the carbon dispersion. At that time, the spray nozzle 9 is moved at a constant speed while increasing the injection amount continuously from the inlet to the outlet of the gas flow path when the unit cell is assembled, and the spray nozzle 3 is the same at a constant injection amount. Moved at speed. The amount of carbon added on the carbon paper from the inlet to the outlet of the gas channel is 1.5 to 2.5 mg / cm.²The injection amount was adjusted so that the fluororesin addition amount / carbon amount continuously increased in the range of 0.25 to 1.0 (weight ratio). In this way, a gas diffusion layer was obtained.
[0067]
  Thereafter, the gas diffusion layer was heated to 350 to 380 ° C. in order to remove the remaining solvent, surfactant and the like. Except for using this gas diffusion layer,referenceThe same operation as in Example 1 was performed. The current-voltage characteristics of the obtained battery are shown in FIG.
[0068]
Comparative Examples 4-6
  Prepare dispersions of fluororesin amount / carbon amount of 0.25, 0.5 and 1.0 (weight ratio),referenceThe spray coating apparatus used in Example 1 has a carbon content of 1.5 to 2.5 mg / cm.²It was uniformly applied on carbon paper so that Except for using carbon paper (gas diffusion layer) with these three types of carbon layers,referenceThe same operation as in Example 1 was performed. The current-voltage characteristics of the obtained battery are shown in FIG.
[0069]
  From FIG. 4, compared with any of the three types of batteries (Comparative Examples 4 to 6) in which the amount of fluororesin added to the carbon layer is uniform, the amount of fluororesin added to the carbon layer is increased from the inlet to the outlet of the gas channel. Continuously increased battery (referenceIt can be seen that the characteristics of Example 2) are superior. This is not only to change the total amount of fluororesin in the carbon layer but also to provide a continuous slope from the inlet to the outlet of the gas flow path in the amount of fluororesin added to the carbon layer. It is effective for improvement.
[0070]
  Here, the fluororesin addition amount / carbon amount is continuously inclined in the range of 0.25 to 1.0 (weight ratio). However, even when this ratio is changed in accordance with the operating conditions of the battery, The same effect was observed if the ratio increased continuously from the inlet to the outlet of the flow path.
[0071]
Example1 and Comparative Examples 7 to 10
  In this example, first, MEA 17 having the structure shown in FIG. 5 was produced. Carbon powder (Vulcan XC72 manufactured by Cabot, USA, primary particle size: 30 nm, specific surface area: 254 m²/ G, DBP oil absorption: 174 cc / 100 g), platinum particles having an average particle size of about 30 mm were supported by 25% by weight to obtain an electrode catalyst. In a solution in which this catalyst powder is dispersed in isopropanol, chemical formula (1):
[0072]
[Chemical 1]

[0073]
A catalyst paste was prepared by mixing a dispersion of perfluorocarbonsulfonic acid powder represented by the formula (1) dispersed in ethyl alcohol.
[0074]
  On the other hand, carbon paper, which is a conductive porous substrate constituting the gas diffusion layer of the electrode, was subjected to water repellent treatment. A carbon non-woven fabric 11 having a thickness of 360 μm (TGP-H-120 manufactured by Toray Industries, Inc.) and an aqueous dispersion of a copolymer (FEP) of tetrafluoroethylene and hexafluoropropylene (Neolon ND- manufactured by Daikin Industries, Ltd.) After impregnating in 1) and drying, water repellency was imparted by heating at 380 ° C. for 30 minutes.
[0075]
  Next, carbon powder (acetylene black HS-100 manufactured by Denki Kagaku Kogyo Co., Ltd., primary particle size: 53 nm, specific surface area: 37 m²/ G, DBP oil absorption: 200 cc / 100 g) was dispersed in the neoflon ND-1 to obtain a paste having a mixing weight ratio of carbon powder and FEP of 87:13. This paste was applied to the surface of the carbon nonwoven fabric 11 that had been subjected to the above-described water repellent treatment, dried, and then heated at 380 ° C. for 30 minutes to form a carbon powder layer 12. At this time, a part of the carbon powder layer 12 was embedded in the carbon nonwoven fabric 11. Thus, the gas diffusion layer 13 which consists of the carbon nonwoven fabric 11 and the carbon powder layer 12 was produced.
[0076]
  On the carbon powder layer 12, the above catalyst paste is applied.TheThe catalyst layer 14 was formed by coating using a clean printing method. In this way, an electrode 16 composed of the catalyst layer 14, the carbon powder layer 12 and the carbon nonwoven fabric 11 was produced.
  The amount of platinum contained in the electrode is 0.5 mg / cm²The amount of perfluorocarbon sulfonic acid is 1.2 mg / cm²It was. This electrode 16 is used for both the anode and the cathode.
[0077]
  Here, the water repellency of the carbon powder (acetylene black HS-100 manufactured by Denki Kagaku Kogyo Co., Ltd.) used for the gas diffusion layer was higher than the water repellency of the carbon powder (Vulcan XC72) used for the catalyst layer. It was. The water repellency was evaluated by the following method.
[0078]
  First, using a doctor blade, carbon powder particles as a test object were applied flatly on the glass surface, and solutions having different surface tensions (mN / m) were dropped therein. It is observed whether the dropped solution soaks inward from the coated surface of the carbon particles or is repelled by the coated surface. Carbon particles repelling a solution with a low surface tension have higher water repellency. For example, the surface tension of water and ethanol is 72 and 22 (mN / m), respectively, and the water repellency of carbon particles that repel both water and ethanol is better than the water repellency of carbon particles that repel water but soak in ethanol. It can be said that it is expensive. The above evaluation results are shown in Table 1. Table 1 shows the physical properties of various carbon particles and the results of the water repellency evaluation. The value described in the column of water repellency is the smallest surface tension (mN / m) of the solution repelled by the carbon particles.
[0079]
  Next, a pair of electrodes 16 and a catalyst layer 14 on the side of the electrolyte membrane 15 are disposed on both sides of a hydrogen ion conductive polymer electrolyte membrane (Nafion 112 manufactured by Du Pont, USA) 15 having an outer dimension 5 mm larger than the electrode 16 described above. It joined by hot press so that it might touch, and MEA17 was obtained.
  The MEA 17 was sandwiched between conductive separator plates to obtain a single cell. The conductive separator plate was obtained by impregnating a carbon plate obtained by cold press molding a carbon powder material with a phenol resin and curing. Thus, the gas sealing property was improved by impregnating the resin. Further, a gas flow path was formed by cutting the carbon plate.
[0080]
  6 and 7 are schematic plan views of a conductive separator plate having a gas flow path (groove) formed on the surface thereof. FIG. 6 shows the shape of the gas passage for fuel gas formed on the surface of the conductive separator, and the gas passage for oxidant gas having the same shape is formed on the back surface. FIG. 7 shows the shape of the cooling water channel formed on the back surface of the conductive separator plate on which the fuel gas gas channel is formed. The separator has a size of 10 cm × 20 cm × 4 mm, and the groove portion 21 constituting the gas flow path is a recess having a width of 2 mm and a depth of 1.5 mm, and the gas flows through this portion. Moreover, the rib part 22 between gas flow paths is a convex part of width 1mm. In addition, a manifold hole for the oxidant gas (injection port 23a, outlet 23b), a manifold hole for the fuel gas (injection port 24a, outlet 24b), and a manifold hole for cooling water (injection port 25a, outlet 25b) were formed. In addition, a conductive gas seal portion 26 in which conductive carbon is dispersed in polyisobutylene was formed.
[0081]
  The MEA 17 shown in FIG. 5 manufactured as described above is composed of the two conductive separator plates shown in FIG. 6, with one fuel gas gas passage facing the MEA 17 and the other oxidizing gas passage. The cell A was obtained by being sandwiched and joined so as to face the MEA 17. Further, the MEA 17 shown in FIG. 5 is composed of the two conductive separator plates shown in FIG. 7 so that one fuel gas flow path faces the MEA 17 and the other cooling water flow path faces the MEA 17. The cell B was obtained by sandwiching and joining.
[0082]
  Next, single cells A and single cells B were alternately stacked one by one, and a total of 50 single cells were stacked to obtain a laminate. A stack was obtained by sequentially stacking a metal current collector plate, an insulating plate made of an electrically insulating material, and an end plate on both ends of the laminate. And the both end plates were fastened with the volt | bolt and nut which penetrated the stack, and the battery module was obtained. The fastening pressure at this time is 10 kgf / cm with respect to the separator plate.²It was. The fastening rod portion for fastening the stack was provided on a side surface different from the side surface where the gas supply / discharge port was open. The battery module thus produced is referred to as fuel cell 1 (Comparative Example 7).
[0083]
  Next, fuel cells having MEAs with different configurations were produced.Comparative Example 7Fuel cells 2 to 8 (Examples) are arranged in a catalyst layer and a gas diffusion layer.1And Comparative Examples 7 to13) Was produced. Components other than carbon powder are:Comparative Example 7It was the same. Table 1 shows the types and physical properties of the carbon powder used. Table 2 shows the carbon material numbers, battery configurations, and battery numbers used for the cathode and anode of the fuel cell. In addition, the particle size of Table 1 is a particle size of a primary particle.
[0084]
[Table 1]

[0085]
[Table 2]

[0086]
[Evaluation]
  Examples above1And Comparative Examples 7 to13The fuel cells 1 to 8 obtained in the above were subjected to a discharge characteristic test.
  Pure hydrogen gas was supplied to the anode of the fuel cell, air was supplied to the cathode, and the cell temperature was maintained at 75 ° C. The fuel gas utilization rate (Uf) was 70% and the air utilization rate (Uo) was 20%. The gas was humidified by passing the fuel gas through a humidified bubbler at 85 ° C and air at 65-70 ° C.
[0087]
  FIG. 8 shows a fuel cell according to an embodiment of the present invention.2And a fuel cell according to a comparative example1, 3 and6 discharge characteristics are shown. FIG. 9 shows the present invention.ComparisonExample fuel cells 4 and 5 and, 7Discharge characteristics of ˜8 were shown. 8 and 9, it can be seen that the fuel cell of the present invention has superior characteristics as compared with the fuel cell of the comparative example.
[0088]
Reference Examples 3-5
  An electrode composed of a catalyst layer and a gas diffusion layer was produced. An acetylene black powder carrying 25% by weight of platinum particles having an average particle size of about 30 mm was used as an electrode catalyst. A dispersion obtained by dispersing the perfluorocarbon sulfonic acid powder represented by the chemical formula (1) in ethyl alcohol was mixed with a dispersion obtained by dispersing the catalyst powder in isopropanol to obtain a catalyst paste.
[0089]
  On the other hand, carbon paper, which is a conductive porous substrate constituting the gas diffusion layer of the electrode, was subjected to water repellent treatment. Acetylene black was dispersed in an aqueous dispersion of fluororesin (Neoflon ND-1 manufactured by Daikin Industries, Ltd.) to obtain a slurry (fluororesin solid content: acetylene black = 1: 1 (weight ratio)). The slurry is applied to a carbon nonwoven fabric (TGP-H-120 manufactured by Toray Industries, Inc.) 11 having a thickness of 360 μm, dried, and heated at 380 ° C. for 30 minutes to obtain a gas diffusion layer having water repellency. It was. At this time, in order to maintain the gas diffusibility and conductivity of the gas diffusion layer, the coating amount of the slurry was adjusted so that the Gurley constant after drying was 1 to 60 (seconds / 100 mL). The Gurley constant was evaluated according to JIS-P8117. If this Gurley constant is small, the gas diffusion layer becomes rough and the conductivity deteriorates. Conversely, if the Gurley constant is large, the gas diffusion layer becomes dense and the gas permeability is deteriorated.
[0090]
  As described above, the catalyst layer was formed on one surface of the carbon nonwoven fabric, which is a gas diffusion layer having water repellency, by applying the catalyst paste using a screen printing method. At this time, a part of the catalyst layer was embedded in the carbon nonwoven fabric. In this way, an electrode 33 having a catalyst layer 32 and a gas diffusion layer 31 was obtained (see FIG. 10). The amount of platinum contained in the electrode is 0.5 mg / cm²The amount of perfluorocarbon carbon sulfonic acid is 1.2 mg / cm²It adjusted so that it might become.
[0091]
  Next, two electrodes 33 are disposed on both sides of the hydrogen ion conductive polymer electrolyte membrane 34 having an outer dimension 2 mm larger than the electrode 33 so that the catalyst layer 32 is in contact with the electrolyte membrane 34 side. For 5 minutes at 38 kgf / cm²These were joined using a hot press at a pressure of 1 to obtain MEA 35 as shown in FIG. Here, as the hydrogen ion conductive polymer electrolyte membrane, a membrane having a thickness of 50 μm made of perfluorocarbon sulfonic acid represented by the above chemical formula (1) (where m = 2) was used.
[0092]
  The MEA produced in this way isComparative Example 7In the same manner as above, a unit cell was obtained by sandwiching from both sides with a conductive separator plate (bipolar plate) in which the gas flow path shown in FIG. 6 or FIG. 7 was formed.
  After stacking two such single cells, a conductive separator having a cooling channel through which cooling water flows was stacked as a cooling unit, and this pattern was repeated and stacked.
  In this manner, a stack of 40 unit cells in total is obtained, and a metal current collector plate, an insulating plate made of an electrically insulating material, and an end plate are arranged at both ends of the stack and fixed with a fastening rod. Got the stack. The fastening pressure at this time is 10 kgf / cm per unit area of the conductive separator plate.²It was.
[0093]
  The manifold shown in FIG. 11 was attached to the stack obtained as described above. As shown in FIG. 11, metal end plates 41 made of SUS304 were arranged on the upper and lower portions of the stack. Insulators 42 were disposed on both sides of the stack, and manifolds 44 and 45 were attached via gaskets 43. The manifold 44 supplies and flows hydrogen to the anode, and the manifold 45 supplies and flows cooling water. In addition, the manifold 46 supplies air to the cathode for circulation. In this way, the present inventionReference example 3A fuel cell A according to the above was produced.
[0094]
  The fuel cell A is supplied with pure hydrogen as a fuel gas through a deionized water bubbler maintained at 75 ° C., and is supplied as an oxidant gas through a deionized water bubbler with air maintained at a predetermined temperature. Went. At this time, fuel gas, oxidant gas and cooling water were all introduced in the same direction, and the gas outlet was opened to normal pressure. Also, the temperature of the fuel cell is maintained at 75 ° C. by adjusting the amount of cooling water, the hydrogen utilization rate is 70%, the oxygen utilization rate is 40%, the hydrogen humidification bubbler temperature is 75 ° C., and the air humidification bubbler temperature is 65 ° C. The current-voltage characteristic test at this time was performed. The results are shown in FIG.
[0095]
  For comparison, FIG. 12 also shows the evaluation results of the fuel cell B in which the Gurley constant of the gas diffusion layer is 0.5 and the fuel cell C in which the Gurley constant of the gas diffusion layer is 70. The configurations of the fuel cell B and the fuel cell C are the same as those of the fuel cell A except for the Gurley constant of the gas diffusion layer.
[0096]
  In FIG. 12, it can be seen that the fuel cell B has a relatively low conductivity, and the fuel cell C has a relatively low gas diffusivity. On the other hand, it can be seen that the fuel cell A has more excellent characteristics than the fuel cells B and C because the gas diffusivity and conductivity are compatible at a high level.
[0097]
  Similarly, when the gas permeability of the gas diffusion layer in the cathode is 1.2 to 2.0 times the gas permeability of the gas diffusion layer in the anode,Reference example aboveExcellent characteristics similar to those obtained were obtained.
  Also, when the porosity of the gas diffusion layer in the cathode is 1.2 to 2.0 of the porosity of the gas diffusion layer in the anode,Reference example aboveExcellent characteristics similar to those obtained were obtained.
[0098]
Reference Example 6
  This reference exampleThen, by changing the thickness of the carbon paper, which is a conductive porous base material constituting the gas diffusion layer, the thickness of the cathode gas diffusion layer is 1.5 times the thickness of the anode gas diffusion layer. IsReference example 3A fuel cell D was produced in the same manner as the fuel cell A of FIG. In this fuel cell D, since a sufficient evaporation area can be secured on the cathode side where generated water must be evaporated, excess water can be discharged safely and quickly, and performance degradation due to wetting can be prevented.
[0099]
  Regarding this fuel cell D,Reference example 3The current-voltage characteristic evaluation test was performed under the same conditions. The result is shown in FIG. In FIG. 13, the fuel cell D of this example is also shown.Reference example 3It has been found that the fuel cell A has substantially the same battery characteristics as the fuel cell A.
[0100]
Reference Example 7
  Reference Examples 3-6In the fuel cell manufactured in step 1, the Gurley constant of the gas diffusion layer is affected by the pressure applied when the MEA and stack are manufactured.Reference example 3In the manufacturing process of the fuel cell A, when the MEA was manufactured by hot pressing, the pressure was adjusted, and the thickness of the gas diffusion layer after pressing was 75 to 90% of the thickness of the gas diffusion layer before pressing.
[0101]
  For fuel cells E, F and G, the pressure during MEA hot pressing is 35, 20 and 50 kgf / cm, respectively.²The fuel cell A was manufactured in the same manner as in the fuel cell A according to Example 8. In this example, the pressure during the hot pressing of the MEA was changed in this way to evaluate this influence, and the result is shown in FIG.
[0102]
  As can be seen from FIG. 14, the fuel with excessive pressureChargeThe pond G has a thickness of about 70% that of the fuel cell E, the gas diffusion layer is buckled, and the gas permeability is extremely lowered. Therefore, the characteristics in the high current density region are lowered. Further, the fuel cell F with a small applied pressure had a thickness of about 130% of the fuel cell E, and the contact resistance increased, so that the voltage decreased overall.
[0103]
Reference Example 8
  This reference exampleThenReference example 3In this stack, the electrode area is further increased, the gas diffusion layer in contact with the ribs is made thin and dense along the gas flow path pattern provided on the conductive separator plate, and the gas diffusion in the portion corresponding to the gas flow path portion The layer was thickened and roughened. A fuel cell H was obtained in the same manner as the fuel cell A according to Example 8, except that the thickness of the dense portion of the gas diffusion layer was 70 to 95% of the thickness of the rough portion.
[0104]
  In the fuel cell H, the gas flowing through the gas flow path reaches the catalyst layer through the gas diffusion layer. Here, if the gas permeability of the gas diffusion layer in the portion in contact with the rib is high, the gas moves between the adjacent gas flow paths through that portion of the gas diffusion layer, and the gas is moved along the gas flow path to the MEA. It will not be possible to supply every corner. In particular, as the area of the electrode is increased, it becomes difficult to supply gas to every corner of the MEA. On the other hand, when the gas permeability is low, the gas supply to the catalyst layer located at the portion corresponding to the rib becomes insufficient, which causes the battery performance to deteriorate. For this reason, the gas permeability of the portion of the gas diffusion layer in contact with the rib needs to be moderately lowered.
[0105]
  The gas diffusion layer plays a role of collecting electrons generated by the reaction, and transports electrons generated in the gas flow path portion to the rib portion. For this reason, if the density of the thick and thin portions of the gas diffusion layer is the same, it is advantageous in terms of conductivity to increase the gas diffusion layer located in the gas flow path portion and increase its cross-sectional area. Become.
  Regarding this fuel cell G,Reference example 3The current-voltage characteristic evaluation test was conducted under the same conditions as in the above. The result is shown in FIG. From FIG. 15, it has a large electrode areaThis reference exampleThe fuel cell H ofReference example 3It can be seen that the fuel cell has substantially the same battery characteristics as the fuel cell A of FIG.
[0106]
Industrial applicability
  As described above, according to the present invention, an excellent polymer electrolyte type having high discharge characteristics, particularly high current-voltage characteristics in a high current density region, by changing the degree of water repellency of the anode and cathode depending on the position. A fuel cell can be obtained. In addition, according to the present invention, by optimizing the water repellency, specific surface area, primary particle diameter, DBP oil absorption amount and the like of the carbon powder in the gas diffusion layers constituting the anode and the cathode, an excellent high performance with high discharge performance can be obtained. A molecular electrolyte fuel cell can be obtained.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a coating apparatus used for spray coating on a conductive porous substrate.
FIG. 2 of the present inventionreferenceIt is a graph which shows the current-voltage characteristic of the cell obtained in the example and the comparative example.
FIG. 3 is a configuration diagram of another coating apparatus used for spray coating on a conductive porous substrate.
FIG. 4 of the present inventionreferenceIt is a graph which shows the current-voltage characteristic of the cell obtained in the example and the comparative example.
FIG. 5 is a schematic longitudinal sectional view of an MEA produced in an example of the present invention.
FIG. 6 is a schematic plan view of a conductive separator plate having a gas flow path (groove) formed on the surface.
FIG. 7 is a schematic plan view of another conductive separator plate having a gas channel (groove) formed on the surface thereof.
FIG. 8 is a graph showing discharge characteristics of fuel cells manufactured in Examples and Comparative Examples of the present invention.
FIG. 9 is a graph showing discharge characteristics of fuel cells manufactured in Examples and Comparative Examples of the present invention.
FIG. 10 was prepared in Examples and Comparative Examples of the present invention.Schematic longitudinal section of MEAIt is.
FIG. 11 is a schematic perspective view of a fuel cell manufactured in an example of the present invention.
FIG. 12 is a graph showing discharge characteristics of fuel cells manufactured in Examples and Comparative Examples of the present invention.
FIG. 13 is a graph showing discharge characteristics of fuel cells produced in Examples and Comparative Examples of the present invention.
FIG. 14 is a graph showing discharge characteristics of fuel cells produced in Examples and Comparative Examples of the present invention.
FIG. 15 is a graph showing discharge characteristics of fuel cells produced in Examples and Comparative Examples of the present invention.

Claims (8)

A cathode and an anode stacked at a position sandwiching a hydrogen ion conductive polymer electrolyte membrane are sandwiched between a pair of conductive separator plates each having a gas flow path for supplying an oxidant gas and a fuel gas to the cathode and the anode, respectively. A polymer electrolyte fuel cell including a unit cell,
The cathode and anode, the catalyst particles, the hydrogen ion conductive polymer electrolyte, a conductive porous substrate and a water repellent, the cathode water repellent rather high than the water repellency of the anode,
The cathode and the anode have a catalyst layer bonded to the hydrogen ion conductive polymer electrolyte membrane, and a gas diffusion layer in contact with the conductive separator plate;
The catalyst layer comprises catalyst particles supported on carbon particles and a hydrogen ion conductive polymer electrolyte,
The gas diffusion layer is made of a conductive porous substrate containing carbon particles,
The water repellency of the carbon particles contained in the gas diffusion layer is higher than the water repellency of the carbon particles contained in the catalyst layer, and the water repellency of at least one of the cathode and the anode varies with respect to the thickness direction,
A polymer electrolyte fuel cell , wherein carbon particles contained in the gas diffusion layer are disposed at a joint portion between the catalyst layer and the conductive porous substrate .   2. The polymer electrolyte fuel cell according to claim 1, wherein the gas permeability of the conductive porous substrate is 1 to 60 seconds / 100 mL in terms of Gurley constant.   The gas permeability of the conductive porous substrate in the cathode is 1.2 to 2.0 times the gas permeability of the conductive porous substrate in the anode. Polymer electrolyte fuel cell.   The porosity of the conductive porous substrate in the cathode is 1.2 to 2.0 times the porosity of the conductive porous substrate in the anode. The polymer electrolyte fuel cell according to any one of the above.   The thickness of the conductive porous substrate in the cathode is 1.2 to 3.0 times the thickness of the conductive porous substrate in the anode. The polymer electrolyte fuel cell according to 1. The specific surface area of the carbon particles contained in the gas diffusion layer, a polymer electrolyte fuel cell according to claim 1, wherein the at 1/2 or less of the specific surface area of the carbon particles contained in the catalyst layer. The particle size of the primary particles of the carbon particles contained in the gas diffusion layer, to claim 1 or 6, characterized in that at least 1.3 times the diameter of the primary particle of the carbon particles contained in the catalyst layer The polymer electrolyte fuel cell as described. High according to claim 1, 6 or 7, wherein the DBP oil absorption of the carbon particles contained in the gas diffusion layer is 2/3 or less of the DBP oil absorption amount of the carbon particles contained in the catalyst layer Molecular electrolyte fuel cell.

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